This invention relates generally to cosmetic emulsions and more particularly to high-viscosity microemulsions based on sugar surfactants, oil components and aluminium-zirconium salts and to their use for the production of cosmetic gel and stick formulations.
Microemulsions are optically isotropic, thermodynamically stable systems which contain a water-insoluble oil component, emulsifiers and water. The clear or transparent appearance of microemulsions is a result of the small particle size of the dispersed emulsion droplets which, for the most part, is under 300 nm, fine-droplet microemulsions brown-red in transmitted light and a shimmering blue in reflected light occurring in the 100 to 300 nm range and optically clear microemulsions occurring in the sub-100 nm range. The droplet size of the macroemulsions is for the most part above 300 nm. By virtue of their greater stability in relation to macroemulsions, the finer distribution of the inner phase, their generally greater effectiveness and the better transdermal penetration of the active principles incorporated therein, microemulsions have acquired considerable significance in the formulation of cosmetic and pharmaceutical preparations. However, their use in water-containing cosmetic gel and stick preparations which can be found on the market as antiperspirant or deodorant products requires a high consistency. Establishing the viscosity of such a system with long-chain polymers often results in loss of the required transparency or in displacement of the thermodynamic equilibrium. Conventional thickeners, mainly polymers, leave the skin feeling sticky after application of the formulations containing them. In addition, antiperspirant or deodorant products are formulated at an acidic pH of ca. 4 and, to this end, require thickener systems that are stable in this pH range, for example polydiols in combination with dibenzylidene sorbitol.
In addition, various antiperspirant sticks based on natural or synthetic waxes in which the active substance is introduced into the wax matrix as a powder have been available on the market for many years. The disadvantage of such sticks is that they are very greasy and often leave a white residue on the skin.
The complex problem addressed by the present invention was to provide high-viscosity microemulsions which would be distinguished by transparency and high stability and which could be used as antiperspirant gel or stick formulations without the adverse sensory effects of large quantities of polymeric thickeners. Oily and aqueous solutions would lend themselves to processing in the formulation, thereby simplifying homogeneous distribution.